Why is my BMW Key Fob Not Working After Battery Change?
Having a BMW key fob suddenly stop working after a battery replacement is frustrating. But don’t panic – in most cases there is a simple fix. This article will walk through the common reasons a BMW key fob may malfunction after changing the battery, along with troubleshooting tips to get you back on the road.
Introduction
Key fobs are convenient wireless remotes that allow you to lock/unlock car doors and even start the ignition from a distance. Over time, the small button battery inside the fob will drain and need replacing. While swapping in fresh batteries is usually straightforward, sometimes the BMW key fob will then stop working for various reasons. [bmw key fob not working after battery change]
Common causes include:
- Incorrectly inserting new battery
- Poor quality or defective replacement battery
- Loss of sync between key fob and car computer
- Undetected physical damage to the fob
By methodically addressing each potential issue and testing the key fob frequently, you can usually get the fob functioning again without having to replace it.
“I was ready to throw my BMW key fob across the garage when it didn’t work after I put in a new battery. Luckily just reprogramming it did the trick.”
Let’s now dive into the various factors that can cause a BMW key fob to malfunction when the battery is changed, plus simple troubleshooting tips to revive yours.
Reasons Why BMW Key Fob May Not Work After Battery Change
Incorrectly Installed Battery
The small lithium “coin batteries” that power key fobs must be inserted properly, with the + and – electrical contacts aligned correctly. If the battery is reversed or upside down, no power will flow to the fob’s circuits.
Always double check that the flat + side of the battery matches the + marks inside the fob during installation. Don’t force in the wrong way.
Gently recheck the battery if the fob will not work, even with a confirmed good battery.
Faulty Replacement Battery
While it’s logical to assume the key fob itself went bad when it stops working, often a defective replacement battery is to blame.
Quality matters when it comes to fob batteries. An improperly manufactured battery may be completely dead right out of the package. Buy name brand batteries from leading manufacturers to minimize getting a “dud”. Big retailers also typically accept returns if a bad battery is suspected.
Cheap no-name batteries from obscure brands commonly have incorrect specifications too, with lower capacity or voltage output than the OEM battery. When shopping, carefully check the battery ratings match what BMW recommends to avoid these issues.
Key Fob Needs Reprogramming/Resynchronization
BMW key fobs utilize advanced encrypted transponder chips to “sync” with the car’s computer system, granting access only to authorized keys. This security sync can sometimes get erased when the battery dies or is disconnected.
Thankfully, BMW has a procedure to follow for resynchronizing and reprogramming a key fob to restore proper function. Owners can often perform resyncing themselves too – check your owner’s manual for the simple process. Typically this involves:
- Sitting in the driver’s seat
- Locking & closing doors
- Performing certain steps to initiate sync mode
- Holding the key fob buttons until confirmation
Follow your model-specific steps when the fob fails after new battery installation.
Damaged Key Fob
Though rare, sometimes key fobs incur physical damage while the battery is being changed. Dropping the fob, prying it open roughly, or handling internal circuit boards may break fragile parts. Diodes or transmitter wires can crack if manhandled, preventing fob signals even with good power.
Closely inspect your BMW key fob unit for external cracks or internal broken components if issues persist after battery replacement. Look for severed or disconnected wires, damaged transmitter modules, and cracked controller boards or buttons.
Gentle handling is required when doing battery replacement to avoid damaging expensive key fob internals!
Troubleshooting Tips
Before giving up on your unresponsive BMW key fob after battery change, methodically test these troubleshooting tips:
- Double check battery orientation – Most common mistake!
- Try brand name battery before assuming fob failed
- Attempt to resync/reprogram between fob & car
- Thoroughly inspect fob for physical damage
Also check your model-specific BMW owner’s guide for further battery and key fob protocols. Persistence and sequentially testing fixes often yields results.
When to Call a Professional
If you have carefully followed troubleshooting tips to no avail, it may be time to consult a professional. BMW dealerships and key fob specialists have advanced tools to properly diagnose issues and may identify simpler fixes.
They can also handle key fob repairs or facilitate replacement if absolutely needed. Costs often exceed $200 for new fobs though, so only opt for this last resort after confirming no other problems exist.
Conclusion
BMW key fobs failing after battery changes usually stem from:
- Incorrect battery orientation
- Faulty or wrong specification replacement battery
- Loss of sync requiring fob reprogramming
- Physical damage from rough handling
Methodically verifying correct battery installation, attempting to resync with car computer, and inspecting for physical damage will restore function for most users.